The invention relates to an electromagnet, comprising a magnet coil which receives an armature movable longitudinally with respect to the coil axis and having an armature rod, and comprising a support of the armature or of the armature rod in a core serving also for the guidance of the magnetic field.
Electromagnets have a wide range of application, for example, as actuating or pressure-regulating magnets. In particular, such magnets are employed, for example, in automatic transmissions of vehicles. Owing to the operating conditions which exist there, in particular in an oil sump, the presence of a high degree of fouling and great temperature differences, the above-described electromagnets are subject to exacting requirements.
The above-described electromagnets are usually constructed in such a way that one or more slide bearings are provided, in particular in the core material of the electromagnet, in order to support and guide the movable element of the electromagnet, namely the armature or the armature rod. As a rule, the bearing is an axial slide bearing which takes up the forces occurring parallel to the coil axis or to longitudinal extent of the rod. These slide bearings or slide-bearing bushes involve a relatively high outlay in respect of mounting. The region which receives the armatures or the armature rod must have a corresponding receiving bore for the slide-bearing bush. For the fitting of the bearing a tolerance must be provided which must be precisely designed in accordance with the bearing quality. This results in a corresponding outlay in respect of the fitting of the bearing.
Since a plurality of slide rings (=as bearings) are also provided for the support of the armature rod, the various bearings must be mounted in an aligned manner. Since a misalignment or radial run-out cannot be ruled out in this case, this also leads to a further tolerance. Since the above-described electromagnets may be employed in areas subject to high temperature fluctuations, these temperature fluctuations must also be taken into account with a corresponding bearing play.
As a result, owing to air-gap losses and frictional hysteresis, the efficiencies of the magnets are relatively poor. Owing to the large bearing play, there is also a susceptibility to fouling and the increased risk of the fouling leading to disruption of the operation of the electromagnet. Moreover, the relatively low precision owing to the large bearing play is also responsible for a relatively poor magnetic circuit, since the bearing plays also lead to relatively large losses at the air gaps which cannot be compensated for. Furthermore, the fitting of the slide-bearing bushes involves a relatively high outlay, since, as described, these bushes require a precise receiving bore. Additional outlay is involved in avoiding an axial displacement of the bearings through the fitting of suitable securing means. Lastly, the fitting of the bearings also takes up additional installation space.
Since the reliability of the above-described electromagnet depends on the accuracy of the support, it is necessary specifically to monitor the support, with corresponding outlay in terms of production and inspection, in order to achieve a satisfactory quality.